Time series pCO2 at a coastal mooring: Internal consistency, seasonal cycles, and interannual variability

Abstract Marine carbonate system monitoring programs often consist of multiple observational methods that include underway cruise data, moored autonomous time series, and discrete water bottle samples. Monitored parameters include all, or some of the following: partial pressure of CO 2 of the water ( p CO 2w ) and air, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH. Any combination of at least two of the aforementioned parameters can be used to calculate the others. In this study at the Gray's Reef (GR) mooring in the South Atlantic Bight (SAB) we: examine the internal consistency of p CO 2w from underway cruise, moored autonomous time series, and calculated from bottle samples (DIC-TA pairing); describe the seasonal to interannual p CO 2w time series variability and air-sea flux ( F CO 2 ), as well as describe the potential sources of p CO 2w variability; and determine the source/sink for atmospheric p CO 2 . Over the ~8.5 years of GR mooring time series, mooring-underway and mooring-bottle calculated- p CO 2w strongly correlate with r -values > 0.90. p CO 2w and F CO 2 time series follow seasonal thermal patterns; however, seasonal non-thermal processes, such as terrestrial export, net biological production, and air-sea exchange also influence variability. The linear slope of time series p CO 2w increases by 5.2 ± 1.4 µatm y −1 with F CO 2 increasing 51–70 mmol m −2 y −1 . The net F CO 2 sign can switch interannually with the magnitude varying greatly. Non-thermal p CO 2w is also increasing over the time series, likely indicating that terrestrial export and net biological processes drive the long term p CO 2w increase.